PET generates images that represent the distribution of positron-emitting nuclides within the body of a patient. When a positron interacts with an electron by annihilation, the entire mass of a positron-electron pair is converted into two 511-keV photons (also referred to as 511-keV events). The photons are emitted in opposite directions along a line of response (LOR). The annihilation photons are detected by detectors that are placed on both sides of the line of response, in a configuration such as a detector ring. The detectors convert the incident photons into useful electrical signals that can be used for image formation. An image thus generated based on the acquired image data includes the annihilation photon detection information.
Modern PET scanners include detectors such as silicon photomultipliers (SiPMs), wherein the detectors are typically tuned such that data collection is normalized for the energy event that is being detected. As explained earlier, the energy events generated have specific energy signature or targets (such as 511-keV, for example), hence the detectors are calibrated to detect the specific energy signature. The SiPM calibration process is typically performed at the component level (during manufacturing of the detectors, for example), at the system level (when the detector is assembled into the imaging system, for example), or in the field (when an imaging module is replaced by a field service engineer or by a user, for example). The calibration process begins by setting an initial anode and cathode bias, and acquiring a gamma ray data (herein also referred to as image, however the data/image corresponds to raw gamma ray data such as energy, position, and timing data). A user then post-processes the acquired data and checks to see if any events are detected, and if events are not detected, then the bias is slowly increased until events are detected, while stopping each time to post-process the image to check for events. This sequence of acquiring a set of data, post-processing the data and further adjusting the bias based on the post-processed data is continued until a desired energy spectrum is obtained and a corresponding calibration bias is determined. Thus, the entire calibration process can take 30-40 minutes with multiple user interventions. Faster and automated calibration methods are desirable.